Cancer is a disease that afflicts many people and is a leading cause of death in humans and non-human animals. Cancers typically involve cells that grow by uncontrolled growth of the cells that creates many new cells. Many anti-cancer drugs are agents that inhibit or stop cell growth.
Many anti-cancer drugs are known to be effective against cancers and tumor cells, but some cancers and tumors respond poorly to these drugs. Further, many anti-cancer drugs also destroy other cells in the body. Thus, new anti-cancer drugs are desired, and drugs that are able to target specific cancer types can provide useful therapeutic options.
Agents that inhibit cell growth are useful as anti-cancer drugs. The National Cancer Institute (NCI) is an agency of the United States government that is involved in the testing of anti-cancer drugs. NCI often conducts initial screening tests of potential anti-cancer drugs using a three cell line test. Each of the three cell lines is a type of cancerous cell. The cells are exposed to the drug candidates, and the drugs' effectiveness in stopping cell growth and/or killing the cells is measured.
The NCI typically tests the most promising drugs with a further battery of approximately about 60 cell lines, which is referred to conventionally as the 60-cell line test, and the dose of the drug that is required to stop cell growth and to kill cells is measured. The dose of the drug that is required to inhibit approximately 50% of the growth of a cancer cell is reported as the GI50 concentration of the drug. The lower the GI50, the more effective is the anti-cancer drug. The GI50 is sometimes reported in the units of −log(GI50), so that the higher the value for −log(GI50), the more effective is the anti-cancer drug. The dose of the drug that is required to stop approximately 100% of cell growth is reported as the total growth inhibition (TGI) concentration of the drug. The dose of the drug that is required to reduce the number of the cells to 50% of the original number of cells is referred to as the LC50 concentration. The lower the TGI or LC50, the more potent is the anti-cancer drug.